Semiconductor wafers are commonly used to create integrated circuits. To transform a wafer into an integrated circuit, a sequence of process steps must be performed on the wafer. These steps are performed using a plurality of processing chambers, each performing one or more specific functions on the wafer. The wafers are moved between the various chambers through the use of one or more robots. In addition, there are components that properly orient the wafers, others that allow wafers to be passed between robots and load locks. This collection of chambers, orientors, pass-through mechanisms, load locks and robots is commonly referred to as a cluster tool.
A Cluster Tool is one example of a Material Transport and Processing System, which transports and processes Materials, such as wafers, in one or more Process stations using a plurality of components including robots, pass-through mechanisms, load locks and others.
In many embodiments, a portion of the cluster tool, including the processing chambers, is maintained in a vacuum state, while the remainder of the cluster tool, including the factory interface or load area, is maintained at normal atmospheric pressure. This configuration requires an interface between these portions, which is commonly referred to as a load lock. The load lock is a specialized chamber, having passageway to both portions, which can be sealed and pressurized as required. Thus, when a wafer is placed in the load lock from the load area, the load lock closes, and pumps down the interior of the load lock to the required vacuum condition, and then opens the passageway into the vacuum portion of the cluster tool. Similarly, as processed wafers exit the cluster tool, the wafer enters the load lock, which is then closed, the chamber is vented to restore normal atmospheric pressure to the load lock and the passageway to the load area is then opened.
In most embodiments, there is a need to have a robot located within the vacuum area to move the wafers between the various chambers. There is also a need to have a robot in the load area to accept new wafers and transfer them to the load lock, and to remove processed wafers from the load lock and return them to the factory interface.
Furthermore, to improve efficiency, wafers are typically processed concurrently, rather than in a serial fashion. Assume a cluster tool has three chambers. If the wafers are processed serially, the first wafer must be processed by all three chambers before a second wafer enters the cluster tool. However, it is most efficient that there be a wafer in each of these three chambers. Thus, once the first wafer has exited the first process chamber and entered the second process chamber, it is desirable to place the second wafer into the first process chamber. Similarly, once the first wafer exits the second chamber, it should enter the third chamber, while the second wafer enters the second chamber and the third wafer enters the first chamber.
Obviously, there is a need to control the flow of these concurrently processed wafers. The movement of the wafers is controlled by the actions of the various robots. Currently, the actions of these various robots are controlled via a single control process. The term “control process” encompasses multiple embodiments, with the requirement that the control process is able to monitor and control the activities of one or more components within the cluster tool. Therefore, this control process can be a dedicated software program executing on a dedicated computer, or a software program executing on a general-purpose computer designed to control the equipment. Alternatively, the control process can be executed on a special purpose machine, specially designed for this purpose. In another embodiment, a control process can run on a computing device that is shared with other similar or dissimilar processes. While the control process is typically a software program executing on a computing device, this is not a requirement. For example, the control process can be a specialized semiconductor component, designed specifically to execute the rules and algorithms described herein.
Currently, a single control process monitors and controls the actions of the various robots, load locks and any other automated equipment used in the cluster tool. In most embodiments, this single control process comprises a software program executing on a dedicated computing platform.
This approach has been highly effective for many years. However, as semiconductor processes continue to become more and more complex, the size and complexity of the associated software has increased by orders of magnitude. When error conditions, sampling requirements, and defect management are considered, the software needed to operate a cluster tool becomes nearly unmanageable. This problem is exacerbated by increases in the number of process steps and process chambers.
A control system for cluster tools that is easily expandable and scalable would be very beneficial. In this way, cluster tools can grow in complexity without the current complication associated with the software.